The invention relates to a process for the reprocessing of sewage sludge.
Because of its organic components, the reprocessing of sewage sludge is performed mostly by combustion whereby the very high water content proves, however, to be a great impairment to the combustion process.
Thus, it has already been suggested that, prior to its combustion, the sewage sludge be subjected to a mechanical partial dehydration or that the sewage sludge be mixed with corresponding volumes of a dry fuel. Both methods have the disadvantage that heat required for the evaporation of the still large volume of residual water is provided disadvantageously at an unnecessarily high temperature level during the combustion.
Thus, it has also already been suggested that the sewage sludge be subjected to a thermal drying prior to its combustion. For this reason, atmospheric fluidized bed dryers e.g. have been introduced in which the heat necessary for the drying process is generated in an atmospheric fluidized bed combustor and is added to the fluidized bed dryer via an intermediate heat transfer cycle. The exhaust vapors produced during the drying process are recycled in part as a carrier medium for the fluidized bed into the fluidized bed dryer and are, for the remainder, condensed outside the installation and are processed correspondingly as an exhaust vapor condensate. Disadvantages of this known process are the relatively high expenditure for process-specific installation parts such as exhaust vapor purifier, exhaust vapor concentrator, exhaust vapor condenser, exhaust vapor condensate processor, and generation and transfer of the required drying heat via pipe walls which are in contact with the exhaust vapors on both sides.